Many orthotic devices have been designed to aid in the support of injured knee joints. Ideally such a device would permit the knee to move through a desired limited range of its own normal motion, but prevent it from moving into other positions which would result in further damage to the joint, such as by twisting or rotation of the leg members about their own axes, or by excessive translational movements, with respect to each other, of the leg members. The normal knee joint motion is essentially rotation about a horizontal axis passing through the knee. However, it has long been known that a simple hinge is unsatisfactory in replicating knee joint function, and a number of more complex structures, some discussed or cited in my U.S. Pat. No. 4,573,455, have been proposed.
One failing of most of the prior art devices has been that they are much too bulky to permit their use in normal activities, particularly where there is bilateral (both legs) involvement requiring two orthoses. Other problems are the failure to follow normal knee joint motion appropriately or apply adequate corrective forces, and the failure to limit extension of the lower leg to an angle required to protect the healing knee joint.
A superior prior art device has been the hinge joint mechanism of my above cited patent. This hinge joint s a polycentric multi-axial articulating series of at least four members, linked one to the other in linear series, with rotation around each axis independently. Such a structure permits any normal knee motion to be followed while it permits rotation and translation in essentially one plane only. That is, twisting of either leg member is prevented.
It has been my experience, during the use of the hinge above described, that a need exists for a similar hinge which restricts translational movement to a somewhat greater extent. In particular, the freedom of motion attained by having at least three independent axes of rotation has proven to be not always necessary. In therapeutic situations requiring a high degree of support it may, in fact, be a disadvantage.
I have now provided an improved hinge joint. Like the preferred embodiment of my previous one, it has four members linked to each other in a three-axial articulating system. However the new system is essentially different. Instead of being a linear series of members, each interior member connected only to the one before it and the one after it, and each rotating independently, the members are more intimately connected, in a non-linear fashion. Further, their rotations are restricted with respect to each other. The result is a hinge joint of great stability. Its motion is bilaterally symmetrical around a center point of the hinge, like a simple one-axis rotation, but it is not equivalent to a simple hinge. The improved joint has proven therapeutically useful in a great number of situations.
The joint is preferably covered with a flexible tubing for comfort of the wearer, to protect the hinge members from contamination by dirt and other foreign substances, and to allow sealed lubrication if desired.
It is an object of my invention to provide an improved hinge system that follows the normal knee joint motion but prevents undesired motions.
Another object of the invention is to provide such a hinge system which is compact but nevertheless exceptionally sturdy.
A further object of the invention is to provide such a hinge system the motion of which is symmetrical about its center but effectively mimics the complex motion of the human knee joint.